1. Field of the Invention
This invention relates to a device for measuring optical properties of samples, in which an integrating sphere is employed and which is applied in a spectrocolorimeter, etc.
2. Description of the Prior Art
In spectrocolorimeters using an integrating sphere and based on diffused illumination, even if they are constructed with the same geometry (d/8 type, for example), certain errors occur between units, not only of different models, but also between those of the same model.
FIG. 4 shows the construction of a conventional device for measuring optical properties of samples, as well as the luminous intensity distribution of said device.
Inner wall 1a of integrating sphere 1 is coated with white powder having high rates of diffusion and reflection. The light beam from light source 11 enters integrating sphere 1 from aperture 16. It first illuminates illuminated area 17 facing aperture 16. After it is diffused and reflected here, it becomes multi-reflected inside integrating sphere 1 and evenly illuminates sample 3 located at aperture 2 for the placement of sample 3.
The light reflected by sample 3 passes through aperture 41, converges by virtue of lens 42 and forms an image on measuring area restriction plate 43. Optical axis 49 of the reflected light is tilted eight degrees away from the normal line of sample 3, constructing so-called d/8 geometry. Aperture 43a located on measuring area restriction plate 43 determines projection 3a on sample 3 as the measurement area.
The light beam passing through aperture 43a converges by virtue of lens 44 and enters one end of optical fiber 45. The other end of optical fiber 45 is connected to a spectrometer not shown in the drawing, which calculates the spectral reflectance of sample 3.
In the above conventional device for measuring optical properties of samples, as shown in the lower half of FIG. 4, luminous intensity 4 of the light illuminating the sample at aperture 2 deviates substantially from perfect diffusion 4i. In other words, of the deviation from perfect diffusion 4i, concavity 4a is attributable to aperture 41 for the measurement and convexity 4b is attributable to the fact that the diffused reflection from directly illuminated area 17, which the light beam from light source 11 first illuminates, directly reaches aperture 2 for the placement of sample 3.
In addition, unevenness is also seen in that the intensity of light incident to the sample at narrow angles is relatively low in comparison with perfect diffusion.
As described above, the luminous intensity of the illuminating light at the sample placement aperture deviates from perfect diffusion despite the use of an integrating sphere, and moreover, this deviation is not uniform between units, regardless whether they are of different models or of the same model. This is because the location of apertures in the integrating sphere and the coating material on the inner wall may be different among different models, and slight errors in the size or location of the apertures or unevenness in coating may exist even among units of the same model.
This invention was made in consideration of the above problem. Its object is to provide a device which, when measuring the optical properties of samples, such as spectral reflectance, accurately measures optical properties of samples without any errors caused by unevenness in luminous intensity of the illuminating light.